Once you join giffgaff you'll get:
Woohoo. Now get double the minutes (500) for only £10 a month. Plus unlimited texts and 1GB mobile internet. Limited time offer.
More info on prices
If you're an iPhone 4 or iPhone 4S user you will need a Micro SIM in order to join giffgaff. The same applies for new Nokia phones such as the Lumia 800 and Lumia 710 and the iPad.